The Work model from the Timesheet module is extended and is used for
creating both projects and tasks. This allows for instance to
transform a task into a project if it gets bigger and need to be
split. The following fields are added to the work model:

Type: Can be Project or Task.

State: Can be Opened or Done.

Parent and Children: Define the tree structure of projects and
tasks.

Party and Party Address: The optional party (and the contact
address) for which the project is made. Available on projects.

Effort: The estimated effort of a task.

Total Effort: Available on projects. Gives the total effort of the
sub-tasks (I.E. tasks of the project and tasks of the sub-projects)
of the current project.

Timesheet Lines: The list of timesheet lines associated to the
current project or the current task.